The pimple can be the start of pox. Is it summer by you and lots of mosquitoes around? If it turns out to be pox, the growth will get larger. After a couple of weeks, will dry up and fall off by itself.
They can get secondary diseases when they have pox. Can you take a flashlight and check inside his beak and deep inside his throat for any unusual yellow or whitish growths? Yellow cheesy growths are one symptom of canker and can be treated with metronidazole. Yeast will show as whitish growths. In the meantime you can put some apple cider vinegar (unfiltered) in the drinking water. 5 ml acv to 1 litre of water.